This invention concerns a novel system for detecting the absence of liquid in a liquid chamber. Such "liquid absence" includes but is not limited to bubbles or liquid level below a predetermined level.
It is often desirable, if not essential, to detect the presence of bubbles in a liquid or the drop in liquid level. For example, in blood processing, such as dialysis, oxygenation, blood fractionation, etc., it is extremely important that the absence of blood resulting from an air leak or any other reason be immediately detected so that the tubing can be clamped before an air bubble is allowed to enter the patient's vein with the blood.
Known in the art are ultrasonic systems for detecting bubbles, in which a signal is transmitted through a liquid chamber containing the liquid and the transmitted signal is received by a receiver after being transmitted through the liquid chamber. The amplitude of the received signal is utilized to determine the presence of bubbles. It is desirable that the system be extremely reliable so that there is minimal chance of error.
To this end, it is an object of the present invention to provide a liquid absence detection system that is very reliable and provides a substantially fail-safe operation.
Another object of the present invention is to provide a liquid absence detection system that is simple in construction and requires a relatively small number of parts.
A further object of the present invention is to provide a liquid absence detection circuit that is efficient to manufacture and easy to repair.
Other objects of the present invention will become apparent as the description proceeds.